This invention relates to an endoscopic television apparatus capable of television-photographing inside a patient's body by using an endoscope.
In endoscopic television-observation of inside a patient's body by means of an endoscope, the output of a light supply unit for supplying illumination light to the endoscope is generally controlled according to the brightness of the region of interest, since th optical density of an image formed on a monitor television may change according to the brightness of the region of interest. In a prior art apparatus, the quantity of light transmitted by the whole or part of an image guide as an image transmitting optical system of the endoscope is measured, and the output of the light supply unit is controlled so as to keep such quantity constant.
In endoscopic television-photographing, however, the quantity of light will greatly change according to the distance between the endoscope and the region of interest so that the television apparatus cannot exercise its faculties despite the aforesaid control of the output of the light supply unit, since the range of photographing distance is wide although the space inside the patient's body is narrow. As a result, an image of a region of the body near the endoscope may become pure white, whereas an image of a region distant from the endoscope may turn out deep-black. Thus, despite the control of the output of the light supply unit, the range to allow satisfactory observation cannot help being quite narrow.